Imperial forces had ravaged the Thousand Sons' homeworld of Prospero following Magnus the Red's breach of the Emperor's Edicts of Nikaea, by flagrantly utilising the forbidden arts of sorcery. Hoping to find some sign of their missing Legion, instead, their squad was taken by surprise when they encountered a much larger force of Traitor World Eaters who were also on Prospero for their own nefarious reasons. In the ensuing conflagration, the majority of the squad were killed and their captain was captured. Utilising his innate precognitive psychic abilities, Sergeant Arvida was able to elude the World Eaters and eventually escape the surface of the Dead World.

Contents

Six solar months after the tragic events of the Fall of Prospero, Captain Menes Kalliston of the Thousand Sons Legion's 4th Fellowship led a squad of Battle-Brothers to the ravaged surface of their homeworld to seek for any signs of Thousand Sons survivors or their Primarch. Instead, this squad was taken by surprise when they encountered a much larger force of Traitor World Eaters led by Assault Captain Khârn, Equerry to his Primarch Angron. The World Eaters were also on Prospero for their own nefarious reasons. In the ensuing conflagration, the majority of the Thousand Sons squad were killed and their Captain was captured. Like all members of the XVth Legion's Corvidae Cult, Arvida was skilled in the psychic discipline of precognition and the determination of the likely probabilities of future events. Despite his bleak circumstances as a captive of the World Eaters, Arvida knew -- as only a Corvidae could be certain -- that death would not find him on Prospero. That was no consolation for all that had been lost, but at least it lent the task of planning his next move a certain urgency. He would survive and live to discover the true causes of his Legion's destruction, and live to fight against them. He would neither pause nor stumble until everything had been revealed to him, everything that would give him a weapon to employ.

Arvida believed Kalliston had been a fool. Coming back to Prospero had been a predictable error, one caused by excessive faith in Magnus. Arvida had never shared that faith, not even when the XVth Legion had been intact. Whatever cataclysm had occurred on Prospero had been beyond Magnus' power to prevent, so it was folly to retain faith in the Primarch's stratagems. Any survivors from the sack of Prospero were alone now, a scattered band of warriors cast adrift on the rip-tides of the galaxy like the spars of a ruined galleon. Arvida had no idea how many of his brothers still lived. Perhaps there were hundreds. Perhaps he was the only one.

Sergeant Arvida somehow managed to evade his pursuers and was later extracted from Prospero by the Space Marines of the White ScarsLegion, who had come to Prospero with their Primarch Jaghatai Khan to learn of Magnus' fate and the truth behind the outbreak of the Horus Heresy.

Sometime later, Arvida came upon the Keshig, the elite 1st Company Veterans of the White ScarsLegion and the Honour Guard to the White Scars' PrimarchJaghatai Khan, while fighting against insectoid Psychneuein. These vile Warp entities were drawn to the mental emanations of unprotected, badly-injured or nascent psykers whose minds they attacked for the obscene purpose of gestating their progeny. Hunted and driven into the wilds far from the glittering spires of Tizca, the destruction of the planet's capital had drawn the fell creatures like moths to a flame. Utlising his innate psychic abilities, Arvida made short work of the foul creatures. Making contact with the Keshig's leader, Qin Xa, Arvida introduced himself as a Sergeant of his Legion's 4st Fellowship and a member of the Corvidae Cult. He explained that he was the last surviving member of his squad, who had become stranded upon the dead world after coming to investigate what had happened to his Legion. Though he wished to depart the now-benighted world, he agreed to assist the White Scars in locating their Primarch, who had fallen into a chasm during the battle with the Psychneuein, if they agreed to let him depart with them.

While searching for the missing Khagan, they later fought against the Death Guard Primarch Mortarion and his Deathshroud. The Deathlord had come to Prospero in order to sway Jaghatai to his side, promising him a position of power in the new order to come after the Traitors deposed the Emperor. The Khagan refused, and soon the two Primarchs were engaged in a titanic battle with one another. While the two forces were engaged, Arvida once again utilised his powerful psychic abilities and created a mental beacon for the White Scars flagship to locate their position and teleport the Loyalists from the surface. Following this Second Battle of Prospero, in recognition for his assistance, the White Scars accepted the Thousand Sons Sergeant as a guest of the V Legion.

As Arvida spent his time recovering from his ordeal on Prospero, he befriended the StormseerTargutai Yesugei. As the Thousand Son slowly regained his strength and precognitive powers, Yesugei repeatedly attempted to convince Arvida to become a member of the V Legion, since the Thousand Sons were now considered Excommunicate Traitoris. He even went so far as to commission his Legion's Artificers to create a hybrid pauldron, incorporating the iconography of both Legions, to replace the one of Arvida's that had been severely damaged during the fighting against the Death Guard. Though Arvida seriously contemplated becoming a part of a Legion once more, he eventually refused -- he would remain, always and forever, a Son of Magnus and a loyal servant of the Emperor. Arvida was determined to follow his fate, for he believed that his destiny was somehow connected to the image of the raven associated with the Corvidae Cult's sigil that he had foreseen while he was stranded on Prospero. During this time, Arvida had begun to experience the mutational effects of his Legion's gene-curse, known as the "Flesh-Change."

Nearly four Terran years later, the White Scars had successfully waged a guerrilla war against the Traitor's supply lines deep in the void. Though their attacks were devastating initially, over time, their numbers were slowly being whittled down to near-critical levels. Following a particularly devastating ambush by the Iron Warriors at Iluvuin, the Khagan was determined to make his way to the Imperial Throneworld, to stand by the Emperor's side when the Warmaster and the Traitors would inevitably invade the Sol System and lay siege to Terra. But they were hindered at every turn -- trapped by the Ruinstorm, the massive Warp Storm conjured by the Word BearersTraitor Legion during the Calth Atrocity, that blocked off large portions of the Milky Way Galaxy to both interstellar travel and communications. They were also constantly being stalked and harangued by Traitor ships from a combined Traitor taskforce comprised of both the Death Guard and the Emperor's Children, led by Lord CommanderEidolon himself.

An opportunity soon presented itself when the White Scars discovered the Kalium Gate, an ancient Warp Gate that dated back to the Dark Age of Technology and had long been abandoned since the Age of Strife. Unfortunately, the White Scars were not able to make use of this Warp Gate, as their tactics and patterns had become predictable to the Traitors, and Lord Commander Eidolon correctly deduced that the White Scars would attempt to utilise the Kalium Gate. By the time the White Scars arrived, they found the Warp Gate was in ruins and that it was teeming with the forces of the enemy. A vicious battle ensued between the two opposing forces. In the ensuring conflict, it appeared that the Khagan had been mortally wounded when he faced the much-changed Lord Commander in battle. But this was merely a feint, as it was actually Keshig Master Qin Xa, wearing the Khagan's armour. Fleeing their attackers aboard the White Scars' flagship Lance of Heaven, Qin Xa would eventually succumb to his wounds.

During this time, Arvida could barely hold back the ravages of the Thousand Sons' mutational Flesh-Change, and each time he utilised his innate abilities, his genetic curse threatened to overwhelm him completely. But before his friend Qin Xa died, he told Arvida to do everything in his power to find a cure for the Flesh-Change. Arvida vowed that he would. It was later revealed that the White Scars presence at the Kalium Gate was merely another diversion, as they had no intention of utilising the Warp Gate, for the Khagan's true purpose was to find the notorious senior Navigator, Novator Pieter Achelieux. Once Novator Achelieux had been found, he led the White Scars to the Catallus Warp Rift, where hidden amongst its turbulent Warp eddies was a long crystalline void station. Within its edifice was an ancient and powerful device known as the Dark Glass, a relic archeotech device from the Age of Technology. Discovered early on by Rogue Traders during the Great Crusade, this device was believed to have been used to test the technology that would later result in the construction of the Golden Throne. The Dark Glass, like its counterpart, could access the Webway through the use of a central throne controlled by a psyker of enormous power to operate.

Still pursued by the forces of the Death Guard and the Emperor's Children, the White Scars discovered the location of the Dark Glass and intended to use it to instantaneously travel to the Sol System. A rogue agent of the Navis Nobilite named Veil, who had accompanied the White Scars, was tasked with the destruction of this archaic device, for it could spell the end of the Navis Nobilite. Targutai Yesugai led a small strike force onto the crystalline space station, desperate to make use of Dark Glass. With the enemy closing in, and the station collapsing all around him due to explosions of Vortex Charges set by Veil, Stormseer Yesugai sacrificed himself by inserting himself into the Dark Glass' command throne and opened a portal to Terra, which allowed the White Scars fleet to swiftly flee through and escape the Traitors' clutches. Before he died, Yesugai's astral form imparted a final message for his friend Arvida -- he asked him to utilise his vast psychic abilities to guide the White Scars' fleet to the Throneworld. As the White Scars' passed through the Immaterium, they were assaulted by hordes of daemons. After he managed to guide the White Scars' fleet closer to Terra, Arvida finally succumbed to the effects of the Flesh-Change and was rendered unconscious. Khalid Hassan, Captain of the Imperial Army's 4th Clandestine Orta and an agent of Malcador the Sigillite, arrived aboard the Lance of Heaven. He promised the White Scars that his master would do everything in his power to treat Arvida's condition, for the Sigillite had been awaiting his arrival.

With his body ravaged by the Flesh-Change, Arvida clung to life by the merest thread. Placed in a stasis sarcophagus, he was taken to the deepest subterranean levels of the Imperial Dungeon, located far below the Imperial Palace. There Malcador attempted to bind a fragment of Magnus the Red's psyche -- one of the many shards of the Crimson King's psychic soul which remained on Terra after he had foolishly utilised a sorcerous spell to break through the psychic shielding of the Imperial extension of the Webway to warn the Emperor of Horus' perfidy. When Magnus breached the Emperor's wards on Terra, his soul was broken -- shattered like a mirror thrown in anger. Effectively his soul had fractured into many aspects that numbered legion. All that remained on Terra was the aspect of the ever-loyal son. One which Malcador hoped to utilise while Arvida's body was in the last stages of the Flesh-Change, in order to resurrect Magnus so that he could take his place upon the Golden Throne and fulfill the destiny the Emperor had originally intended for His psychically-potent son --to connect the myriad worlds of the Imperium with a human version of the AeldariWebway.

Worried at what was being done to Arvida, Jaghatai Khan rushed to his aid and ordered the Sigillite to stop what he was doing -- but it was already too late. As the shard of Magnus was too powerful to contain, Arvida's severely mutated body began to be consumed by psychic fire. Malcador intended to euthanise the Sorcerer, but the Khagan insisted that Arvida was his ward and must be given a chance to succeed or fail on his own, without any outside interference. The Primarch then proceeded to destroy the arcane machinery in the chamber, freeing the amalgam Magnus/Arvida from the suppression fields and psychic wards.

The energy that consumed Arvida's body soon coalesced and solidified into solid matter, taking the form of an Astartes, but without any sign of the Flesh-Change. One of the being's eyes was swollen with scar tissue, much like the Crimson King's own missing eye. This entity was not the shadow-Primarch trapped in a host body like Malcador had intended, nor was he entirely the Legionary formerly known as Revuel Arvida, for he had become much more. When referring to himself, he asked to be called "Ianus". Ianus apologised for not becoming Magnus due to the fact that they both were going to end up dying in the near-future.

The name Ianus would later be transcribed as "Janus," one of the eight Space Marines chosen by Malcador the Sigillite and approved by the Emperor to lay the foundation of what was to become the Inquisition and the Grey KnightsChapter of the Space Marines. Years later, following their personal audience with the Master of Mankind in the final days of the Horus Heresy, Malcador took the eight Space Marines to the moon of Saturn called Titan, and oversaw the initial creation of the Grey Knights as a fully-functioning Chapter. But the Sigillite could not remain to oversee their evolution, so he selected one of the eight to lead the Chapter in the years to come.

Malcador's final act before returning to Terra for the climax of the Heresy was to appoint Janus as the first Supreme Grand Master of the Grey Knights, to guide the nascent Chapter through its first challenges. Legends of the Grey Knights' founding lord are as numerous as there are stars in the night sky -- the champions he slew, the wars he won, the daemons he banished -- and none alive now know how much they have been twisted through the centuries.

Over a thousand Terran years later, at the conclusion of the War of the Beast in 546.M32, the Grand Master of Assassins, Drakan Vangorich, purged eleven of the High Lords of Terra, in an event that came to be known as The Beheading. Vangorich then appointed himself the Lord Protector of the Imperium. The last surviving High Lord, Inquisitorial RepresentativeMarguerethe Wienand, was spared by Vangorich. She was made aware of the existence of the Ordo Malleus' Chamber Militant -- the Grey Knights Space Marine Chapter -- and was urged to seek out their leader Janus -- shortly before the death of her co-representative Veritus, who had been slowly poisoned by Vangorich over a matter of solar days. Veritus gave Wienand the key to the Citadel of Titan and named her his successor. She would be the liaison between the Inquisition and the secretive Grey Knights Chapter. Upon meeting Janus for the first time, though she had encountered many Space Marines during her lifetime, she was nearly overcome by the Supreme Grand Master's sheer presence, for he was more than a simple Astartes, he was the everything the Crimson King should have been. Together, they would unleash the power of the Grey Knights upon the enemies of Mankind, the final gift of the Emperor to the people he loved.

Arvida is a Nordic name that is the feminised form of Arvid. This name derives from the Old Norse "Arnviðr", itself drawn from proto-Germanic roots, composed of two elements: "*arnu- / *arô” (eagle) plus "*widu-" (forest, wood, tree). This translates as "forest of eagles."

The name Ianius is derived from the Latin "Iānus", meaning "divine gate, gate to heaven." Ianus is also a genus of moths which have a tendency to metamorphose from a pupa into a full-grown moth, a possible allusion to Arvida's transition from a former Thousand Sons Astartes into Ianus.

In ancient Roman religion and myth, Janus is the god of beginnings, gates, transitions, time, duality, doorways, passages, and endings. He is usually depicted as having two faces, since he looks to the future and to the past.